<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style type="text/css">
        .menu {
            width: 960px;
            height: 80px;
            background-color: gold;
            position: fixed;
            line-height: 80px;
            top: 0px;
            left: 50%;
            /* text-indent: 40px; */
            margin-left: -480px;
        }

        p {
            text-align: center;
        }

        .popup {
            width: 500px;
            height: 300px;
            border: 1px solid #000000;
            background-color: white;
            color: white;
            position: fixed;
            left: 50%;
            margin-left: -250px;
            top: 50%;
            margin-top: -150px;
            z-index: 9999;

        }

        .popup h2 {
            background-color: gold;
            margin: 10px;
            height: 40px;
        }

        .mask {
            position: fixed;
            width: 100%;
            height: 100%;
            background-color: #000000;
            left: 0;
            top: 0;
            opacity: 0.5;   /* 透明度 */
            z-index: 9998;  /* 优先显示级别 */
        }
        .pop_con{
            display: none;
        }
    </style>
</head>

<body>
    <div class="menu">菜单文字</div>
    <br>
    <br>
    <br>
    <br>
    <br>
    <br>
    <div class="pop_con">
        <div class="popup">
            <h2>弹窗的标题</h2>
        </div>
        <div class="mask"></div>
    </div>
    <!--     <p>网页文字</p>
    <br>
    <br>
    <br>
    <br>
    <br>
    <p>网页文字</p>
    <br>
    <br>
    <br>
    <br>
    <br> -->

</body>

</html>